1. Field of the Invention
The present invention relates to a respiration monitoring system which is capable of continuously monitoring the respiratory state of a person such as a patient through visual sensing in a non-restrictive manner. It also relates to an apparatus for setting a region of interest for respiration monitoring.
2. Description of the Related Art
In recent years, the number of persons of advanced age has rapidly increased, and thus the number of staff members caring for bed-ridden elderly persons has likewise increased, thereby increasing personnel costs therefore and medical care expenditures. Such increased costs have become an object of great public concern.
Accordingly, it has hitherto been known that respiration monitoring systems have been developed which are capable of continuously monitoring the respiratory state of a bed-ridden aged person and the like through visual sensing in a non-restrictive manner.
FIG. 13 diagrammatically shows a typical example of a conventional respiration monitoring system entitled "Automatic Measurements of the Number of Respirations under Complete Non-restrictions by a Visual Sensing System" that was reported in the proceeding of the 16th Bio-Mechanism Society Conference held on Nov. 25, 1995 by the Bio-Mechanism Society on pages 279 through 282.
This respiration monitoring system includes a CCD camera 2 for imaging or photographing the chest of a patient 1 as an object to be imaged who is lying on a bed, an image processor 3 connected to an output of the CCD camera 2 for successively extracting an inter-image difference or subtraction (i.e., subtraction between every two successive images) of continuous motion pictures at a constant period of time and performing predetermined image processing so as to obtain or calculate a changed component to thereby measure the number of respirations per unit time, a monitor 4 connected to an output of the image processor 3 for displaying a visual indication of the detected data including the measured number of respirations per unit time, the state of respiration and/or displaying an abnormal state in the case of an abnormality taking place, and a setting input section 5 through which an operator can input various settings such as a processing region in the form of a region of interest (hereinafter simply referred to as ROI) of the image processor 3, an interval of subtraction (.alpha.) in the image processing, etc.
FIG. 14 is a flow chart showing an operation (i.e., respiration counting operation) of the above-mentioned conventional respiration monitoring system.
Now, the operation of the conventional respiration monitoring system will be described in detail while referring to the flow chart of FIG. 14.
First in step S1, the image processor 3 successively receives image data from the CCD camera 2, and in step S2, it performs signed (+, -) subtraction of pixels between every two adjacent images that are spaced a predetermined distance from each other in the form of a frame interval (.alpha.). Subsequently, in step S3, the image processor 3 performs surface integration within a ROI. Specifically, the surface integration is carried out as follows. The image data extracted are subjected to signed subtraction (i.e., subtraction with a plus or minus sign) to provide binarized images, from which an area of variations for each image is calculated. Each area thus obtained is then surface integrated in terms of brightness to provide a signed changing speed or rate of each changed portion. Then, in step S4, the signed changing speed thus obtained is processed in a time-series manner each time the CCD camera 2 takes one frame, on the basis of the result of which respiration counting is carried out in step S5.
In this manner, the conventional respiration monitoring system can monitor the state of respiration through visual sensing in a non-restrictive and continuous manner.
With the above-mentioned respiration monitoring system, however, a watch man or supervisor who also acts as an operator has to manually input the setting of a specific region of interest (ROI) among the pictures or images photographed by the CCD camera 2, for which region image processing is to be performed for measuring or counting the number of respirations per unit time, while watching the monitor 4, as referred to above.
Thus, with the conventional respiration monitoring system in which the ROI setting is input manually by an operator, if, for example, a person such as a patient to be monitored or photographed has moved to displace the ROI, it becomes unable, if not impossible to measure or count the number of respirations per unit time in an accurate manner or the respiration measurement or counting becomes impossible when such a situation is left unattended. As a result, it will be impossible to automatically measure the respiration for a long period of time. On the other hand, if the deviation or displacement of the ROI (i.e., movement of the person) is monitored by the watch man in order to make it possible to effect a long-term accurate respiration counting, it becomes impossible to achieve the intended purpose of reducing the personnel expense and the amount of labor required through automatic respiration counting.
Moreover, in this case, a change in the value of surface integration becomes small depending upon the position of setting of the ROI, so the accuracy of respiration counting can be reduced due to influences of noise or the like, or it will be difficult to recognize inhalation and exhalation of the person on a monitor.
Furthermore, with the conventional respiration monitoring system, the frame interval .alpha. for subtraction is also set and input by the operator, so similar to the setting of the ROI, it is difficult to perform long-term respiration counting. In addition, the frame interval .alpha. is input by the operator based on his or her experience, so the accuracy of respiration counting depends on the setting for .alpha. and sometimes decreases due to an inappropriate setting, with the result that recognition of inhalation and exhalation on the monitor becomes difficult.
Further, the conventional respiration monitoring system calculates the speed or rate of change in the darkness or gray level within the ROI using an inter-image subtraction with a plus or minus sign, and hence, if an increase and a decrease of brightness within the ROI are equal in their areas to each other, it is determined that there is no change in the speed.